Vibratory work machines such as compactors are often employed to compact soil, gravel, asphalt, and other materials. These vibratory work machines include plate-type compactors and rotating drum compactors. A typical drum compactor has a drum assembly with one or more drums for compacting the material. The drum assembly includes a vibratory mechanism having two or more weights arranged on a shaft rotatable about a common axis within an interior cavity of the drum for inducing vibrations on the drum. The weights are eccentrically positioned with respect to the common axis and are typically movable with respect to each other about the common axis to produce varying degrees of imbalance during rotation of the weights.
The vibratory mechanism provides one or more frequency and amplitude settings. In operation, the vibration amplitude and frequency of a compactor may be changed by a user to suit a particular application. The suitable amplitude and frequency of the vibration may vary depending on the characteristics of the material to be compacted. For example, the vibration amplitude and frequency suitable for compacting gravel for a road may be different from the vibration amplitude and frequency suitable for compacting soil for a footpath. Also, a compacting process may often require compaction with different amplitude and frequency levels at the beginning and end of the process. Furthermore, when a material such as asphalt cools down, its hardness often changes. As a result, compaction with different amplitude and frequency levels may be required based on the temperature of the material.
Vibration amplitude and frequency determine the quality of the compaction, as well as the efficiency of the compaction process. Typically, the amplitude of the vibrations produced by the eccentric weights in the drum assembly may be varied by positioning the weights with respect to each other about their common rotational axis to vary the average distribution of mass (i.e., the centroid) with respect to the rotational axis. In general, vibration amplitude increases as the centroid moves away from the rotational axis of the weights and decreases toward zero as the centroid moves toward the rotational axis. It is also known that varying the rotational speed of the weights about their common axis may change the frequency of the vibrations.
A known vibratory mechanism allows a user to select a desired vibration frequency from one or more possible frequencies independent of the selection of a desired vibration amplitude. In some cases, the vibratory mechanism may enable the user to adjust only vibration amplitude while a vibration frequency remains fixed or uncontrolled, or may enable the user to adjust only vibration frequency while vibration amplitude remains fixed or uncontrolled. For example, U.S. Pat. No. 4,481,835 discloses a device that can continuously adjust a vibration amplitude. However, these known vibratory mechanisms do not establish any relationship or dependency between vibration frequency and vibration amplitude. As a result, a user may be permitted to inadvertently select a vibration frequency and amplitude combination that results in unintended decoupling. Decoupling occurs when a compactor vibrates with a vibratory amplitude that is high enough that the compacting drum becomes airborne.
Thus, the present control system is directed to solving one or more of the shortcomings associated with prior art designs and providing a system and method for controlling a vibratory mechanism with more stability and less interference with the machine performance.